A two-day storm is expected to deliver moderate snowfall and winds to the region. Heightened avalanche danger will exist in the mountains during the storm.
Confidence
Low - Due to the number of field observations
Weather Forecast
Thursday: 10-15cm new snow expected with moderate winds from the southwest. Freezing level will sit near 1400m. Friday: 15-25cm of new snow expected with SW winds continuing and intensifying. Saturday will see some clearing with snowfall ending and cooler temperatures.
Avalanche Summary
Reports from Monday included a remotely-triggered, 20-40 cm thick, Size 2 wind slab avalanche on a SE facing alpine slope in Rogers Pass. Check the Glacier National Park Avalanche Forecast for more details. As of Wednesday, Nov 23rd, no new avalanche observations have been reported.
Snowpack Summary
Recent reports suggest snowpack depth is 100-190cm in the alpine and 80-140cm at treeline. The snowpack below treeline remains below threshold for avalanches, so early season hazards such as hidden rocks, stumps, and open creeks exist. Up to 50cm of recent storm snow is settling into a cohesive slab over a hard crust. Some reports suggest new snow is bonded well to this crust, however the potential exists for this layer to be triggered with heavier loads, including the forecast snowfall amounts. Southerly winds have formed wind slabs on lee features below ridgetops in exposed terrain. The mid and lower snowpack layers are mostly well-settled.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.